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SSD caching has been around for a long time, as a way to reap many of the performance benefits of fast storage without completely abandoning the high capacity and lower prices of slower storage options. In recent years, the fast, small, expensive niche has been ruled by Intel's Optane products using their 3D XPoint non-volatile memory. Intel's third generation of Optane Memory SSD caching products has arrived, bringing the promise of Optane performance to a new product segment. The first Optane Memory products were tiny NVMe SSDs intended to accelerate access to larger slower SATA drives, especially mechanical hard drives. Intel is now supporting using Optane Memory SSDs to cache other NVMe SSDs, with an eye toward the combination of Optane and QLC NAND flash. They've put both types of SSD onto a single M.2 module to create the new Optane Memory H10.

The Intel Optane Memory H10 allows Intel for the first time to put their Optane Memory caching solution into ultrabooks that only have room for one SSD, and have left SATA behind entirely. Squeezing two drives onto a single-sided 80mm long M.2 module is made possible in part by the high density of Intel's four bit per cell 3D QLC NAND flash memory. Intel's 660p QLC SSD has plenty of unused space on the 1TB and 512GB versions, and an Optane cache has great potential to offset the performance and endurance shortcomings of QLC NAND. Putting the two onto one module has some tradeoffs, but for the most part the design of the H10 is very straightforward.

The Optane Memory H10 does not introduce any new ASICs or any hardware to make the Optane and QLC portions of the drive appear as a single device. The caching is managed entirely in software, and the host system accesses the Optane and QLC sides of the H10 independently. Each half of the drive has two PCIe lanes dedicated to it. Earlier Optane Memory SSDs have all been PCIe x2 devices so they aren't losing anything, but the Intel 660p uses a 4-lane Silicon Motion NVMe controller, which is now restricted to just two lanes. In practice, the 660p almost never needed more bandwidth than an x2 link can provide, so this isn't a significant bottleneck.

With a slow QLC SSD and a fast Optane SSD on one device, Intel had to make judgement calls in determining the rated performance specifications. The larger two capacities of H10 are rated for sequential read speeds in excess of 2GB/s, reflecting how Intel's Optane Memory caching software can fetch data from both QLC and Optane portions of the H10 simultaneously. Writes can also be striped, but the maximum rating doesn't exceed any obvious limit for single-device performance. The random IO specs for the H10 fall between the performance of the existing Optane Memory and 660p SSDs, but are much closer to Optane performance. Intel's not trying to advertise a perfect cache hit rate, but they expect it to be pretty good for ordinary real-world usage.

The Optane cache should help reduce the write burden that the QLC portion of the H10 has to bear, but Intel still rates the whole device for the same 0.16 drive writes per day that their 660p QLC SSDs are rated for.